A series of mutants, some temperature-sensitive, which are defective in transformation of Bacillus subtilis, have been isolated following ethyl methane sulfonate treatment of purified spores. Of particular interest are those mutants which are no more sensitive to mitomycin C and methyl methane sulfonate than wild type. The mutants are being examined to determine the stage at which DNA processing for transformation is blocked. Those mutants defective in early steps of transformation are being selected for future studies. Thus the activities of the endodeoxyribonuclease and other nucleases will be determined in these mutants in order to evaluate the role of nucleases in the early processing of DNA. The mutational sites will be mapped in relation to other chromosomal markers by phage PBS-1 transduction. BIBLIOGRAPHIC REFERENCES: Burke, Jr., W.F. and Spizizen, J. Purification and properties of the heat-activated endonuclease in Bacillus subtilis. Abst. Annu. Meet. Amer. Soc. Microbiol. p. 157, l976. Burke, Jr., W.F. and Spizizen, J. Characterization of the heat-activated endonuclease in Bacillus subtilis. Fed. Proc. 35: 1619, l976.